Semiconductor Device and Method for Evaluating Semiconductor Device

Abstract

A semiconductor layer with a low density of trap states is provided. A transistor with stable electrical characteristics is provided. A transistor having high field-effect mobility is provided. A semiconductor device including the transistor is provided. A method for evaluating a semiconductor layer is provided. A method for evaluating a transistor is provided. A method for evaluating a semiconductor device is provided. Provided is, for example, a semiconductor layer with a low defect density which can be used for a channel formation region of a transistor, a transistor including a semiconductor layer with a low defect density in a channel formation region, or a semiconductor device including the transistor.

1 - 10 . (canceled) 
     
     
         11 . A semiconductor device comprising:
 a transistor including an oxide semiconductor layer in a channel formation region, the oxide semiconductor layer being electrically connected to a first electrode and a second electrode,   wherein, while a voltage is applied between the first electrode and the second electrode, the oxide semiconductor layer begins to be irradiated with light having a peak intensity in a wavelength range of 340 nm to 360 nm and an intensity of 3 mW/cm 2  at a temperature of 25° C. at a time T 0  and irradiation is stopped at a time T 1 ,   wherein a value of a current flowing between the first electrode and the second electrode at a time T 2  is greater than or equal to 70% and less than 100% of a maximum value of a current flowing between the first electrode and the second electrode between the time T 0  and the time T 1 ,   wherein a value of a current flowing between the first electrode and the second electrode at a time T 3  is greater than or equal to 5% and less than 100% of the maximum value of the current flowing between the first electrode and the second electrode between the time T 0  and the time T 1 ,   wherein the time T 2  is after a period of greater than or equal to 1 second and less than or equal to 15 seconds from the time T 0  and before the time T 1 , and   wherein the time T 3  is after a period of greater than or equal to 1 second and less than or equal to 15 seconds from the time T 1 .   
     
     
         12 . The semiconductor device according to  claim 11 ,
 wherein the time T 2  is five seconds after the time T 0 , and   wherein the time T 3  is five seconds after the time T 1 .   
     
     
         13 . The semiconductor device according to  claim 11 ,
 wherein the time T 1  is after a period of greater than or equal to 100 seconds and less than or equal to 300 seconds from the time T 0 .   
     
     
         14 . The semiconductor device according to  claim 11 ,
 wherein the oxide semiconductor layer includes a first oxide semiconductor layer and a second oxide semiconductor layer over the first oxide semiconductor layer, and   wherein the second oxide semiconductor layer has a lower electron affinity than an electron affinity of the first oxide semiconductor layer.   
     
     
         15 . The semiconductor device according to  claim 11 , further comprising an insulating film in contact with the oxide semiconductor layer and a third electrode overlapping with the oxide semiconductor layer with the insulating film interposed therebetween. 
     
     
         16 . The semiconductor device according to  claim 11 ,
 wherein the oxide semiconductor layer comprises at least indium.   
     
     
         17 . (canceled)